Air handling in cell culture vessels with little or no headspace is problematic. Some cell culture vessels designed to be filled entirely or nearly entirely with liquid culture medium have caps that seal to prevent leaking. However, as the vessel experiences, for example, temperature swings, gas and vapor pressure changes in the vessel can lead to distortion of the vessel and decrease integrity of the vessel. Accordingly, it would be desirable to provide a vent for such systems. Such vents should include a microbial filter to prevent contaminated air from entering the cell culture environment. However, such vents do not work properly when wet and it is difficult to keep the filters dry in systems with limited headspace.